1. Field of the Invention
The invention relates to vacuum deposition, and more particularly to a system and method for vacuum deposition in a cluster tool.
2. Description of the Related Art
Vacuum evaporation systems are well known in the art. FIG. 1A illustrates a typical vacuum evaporations system 10, which has magnetron sputtering and/or electron beam gun deposition capabilities. Magnetron sputtering and electron beam gun deposition are well established technologies for the coating of objects, such as semiconductor substrates. For example, sputtering is accomplished by bombardment with high-energy ions, usually ions of the rare gas argon (sputter gas), which is initiated by gas discharge processes. The ions of the sputter gas are subjected to controlled acceleration in the direction of the target at high kinetic energies, such that individual atoms can be knocked out of the target.
As illustrated in FIG. 1A, vacuum deposition system 10 includes a single closed chamber 12 operatively coupled to a roughing pump (not shown) and a diffusion type pump (not shown) through a series of valves 18a-18d. The sputter process is typically carried out in closed chamber 12 under conditions of deep vacuum pressures to ensure a long to mean free path length of the vapor particles (i.e., sputtered particles) as possible.
FIG. 1B illustrates a representative Pressure-Time profile for system 10. As shown, valves 18a-18d are closed to maintain the pressure in chamber 12 initially at atmospheric pressure. Valve 18a is opened to allow the roughing pump to lower the pressure in chamber 12 to a first pressure P0. Once the pressure is lowered to a level where the roughing pump is no longer effective, valve 18a is closed while valves 18b and 18c are opened to allow the diffusion pump to evacuate chamber 12 down to deep vacuum pressure P1. Since in most evaporation processes the process is not controlled, the deep vacuum pressure supplied by the diffusion pump is necessary to compensate for the increase in pressure that occurs at time T3, when the evaporation process begins. Also, since the mean free path of the sputtered particles is longest at pressures below pressure P0, the deep pressure is necessary to increases the length of time that the sputtered particles can be effectively deposited.
Unfortunately, because of the rapid increase in pressure during the evaporation process, the mean free path of the sputtered particles is changing from long to short very quickly, which can create a relatively non-uniform deposition. Another drawback of vacuum deposition system 10 is the inefficient use of the vacuum pumps. For example, the roughing vacuum pump is effective to evacuate chamber 12 up to pressure levels of from 0.7 Torrxe2x88x920.5 Torr. At pressure levels of 0.7 Torrxe2x88x920.5 Torr the efficiency of the mechanical pump is reduced dramatically because the movement of the remaining atmosphere in chamber 12 begins to take on molecular flow characteristics. This results in a substantial reduction in pumping speed as chamber 12 continues to be evacuated to about 0.2 Torr. The diffusion pump can then be used to further evacuate chamber 12 to the desired deep vacuum pressure levels. Unfortunately, since diffusion pumps, such as oil diffusion pumps, are ineffective when operated at pressures over 0.2 Torr microns, chamber 12 has had to be mechanically evacuated to the effective operating range of the diffusion pumps. The time taken to reduce the pressure in chamber 12 from 0.5 Torrxe2x88x920.2 Torr can be significant and can reduces production rates appreciably. In addition, once the evaporation process has begun, the pressure in chamber 12 rises significantly, which is usually above the operating range of the diffusion pump. This prevents the ability to continuously process substitutes.
In addition to the length of time required to evacuate chamber 12 to its effective operating levels, chamber 12 is opened to atmosphere between operations. The evacuation time is further extended since water and oxygen molecules, as well as other contaminants, are introduced into chamber 12. The presence of these contaminants can adversely effect the quality of the thin film layers. Purging chamber 12 of such molecules is possible, however, this further extends the production time.
What is needed is a vacuum deposition system that provides a continuous processing capability, reduces processing cycle times, and increases throughput per cycle.
The present invention provides a processing system and associated method for vacuum evaporation of material onto a substrate. In accordance with the present invention, the system includes an evacuation system arrangement for evacuating the processing system to adequate processing pressure levels. Advantageously, the evacuation system arrangement includes pumps, which are capable of substantially maintaining the processing pressure levels for continuous thermal evaporation processing without the need for lowering the pressure to deep vacuum pressure levels. The processing system further includes a loading chamber, a transfer chamber, and a thermal evaporation processing chamber arranged together to form a cluster tool. The cluster tool arrangement provides the system a continuous processing capability.
In one aspect of the present invention, a system is provided for vacuum depositing a thin film on a semiconductor substrate. The system includes a wafer processing chamber for receiving a substrate. The wafer processing chamber defines a transfer section and a processing section. The transfer section provides the system with the capability to insert and remove substrates on a continuous cycle. The processing section provides the system with a thermal evaporation processing capability in which the thin film is deposited on the substrate. A first evacuation device is provided in the system for evacuating the wafer processing chamber to an operating pressure. A second evacuation device is also provided for evacuating the wafer processing chamber to sustain the operating pressure throughout the wafer processing cycle. Once the processing of the substrate has occurred, the substrate can be transported between the transfer section and the processing section while the chamber is maintained at or near the operating pressure.
In another aspect of the present invention, a method is provided for vacuum depositing a thin film on a substrate. The method includes providing a wafer processing chamber for receiving a substrate. The chamber is substantially and continuously evacuated to sustain a selected operating pressure level during a thermal evaporation process, which may be conducted in the wafer processing chamber.
The present invention has many advantages over typical vacuum deposition systems and methods. For example, sputtered particles that emanate from the evaporated material during the evaporation process have a more average and consistent mean free path. Thus, the sputtered particles can be more uniformly deposited on the wafer. Because the present invention does not require deep vacuum pressure levels, the process chamber structure can be made smaller and more economically. By avoiding the need for deep vacuum pressures, the system of the present invention can be arranged in conjunction with a loading station and a transfer station to provide continuous cycling of substrates within a closed vacuum environment. Thus, exposure of the substrates to contamination is minimized and processing cycle times are reduced. The time needed to reduce the chamber pressure to deep vacuum levels and the need to backfill the chamber between processing cycles is removed, thus throughput of processed substrates can be increased.
These and other features and advantages of the present invention will be more readily apparent from the detailed description of the embodiments set forth below taken in conjunction with the accompanying drawings.